1. Field of the Invention
This invention relates to a remote control apparatus for maintaining in-vessel components in a structure having an inner torus space, and in more particular to a remotely controlling maintenance apparatus adapted for a tokamak type nuclear fusion reactor.
2. Description of the Related Art
With a nuclear fusion reactor in which a D-T reaction occurs, the maintenance of the in-vessel components must always be remotely controlled in order to protect the operator from radiation produced in the reactor after it begins to be run.
As shown in FIG. 34 the tokamak type nuclear fusion reactor has a hollow donut shape vessel 1, the torus space 2 of which has an outer diameter of substantially 10 meters and which is covered with a shield member 3 having a thickness of several meters. The peripheral components such as a toroidal coil 4 and a poloidal coil 5 surround the inner torus space 2 in a complicated manner. Accordingly, it is necessary to insert a maintenance device housed in a cask 8 disposed outside of the reactor into the torus space 2 through maintenance ports 9 each extending radially of the torus space 2 and further to move the maintenance device in the circumferential directions in the space 2 so that the maintenance device is accessible to the in-vessel components such as diverter plates 6 and first wall armor tiles 7 without interference with the peripheral components. Since the in-vessel components include very heavy components such as the diverter plate weighing more than 1 ton, these heavy components impose many technical problems on a maintenance device.
The conventional maintenance devices are classed into two types. One of them has, as shown in FIG. 35, a cantilever type multi-joint arm (articulated arm) 10 which has its base joint disposed at the outside of the reactor. The arm 10 is inserted in the torus space 2 through the maintenance port 9 to have access to the in-vessel components. The maintenance devices of this type have been used in the United states and Europe. However, as the vessel becomes larger and larger, the articulated arm becomes longer and longer. In addition, the in-vessel components to be handled become heavier. These make it difficult to accurately set the distal end of the articulated arm 10 at a required position. Further, the maintenance device of this type has the problem that its operational efficiency and reliability are lowered because the long overall articulated arm 10 must be moved in the narrow torus space 2 at each time when the in-vessel components are handled. An example of the maintenance devices of this type is disclosed in the thesis titled "THE TFTR MAINTENANCE MANIPULATOR" by M. Selig et al (Proceedings of a Technical Committee Meeting on Robotics and Remote Maintenance Concepts for Fusion Machines -Karlsruhe, 22-24 February 1988- issued by The International Atomic Energy Agency).
The maintenance device of the other type has a vehicle which runs on a rail laid in the torus space so that the vehicle is accessible to the in-vessel components to handle them. The maintenance device of this type has the features that the positioning of the vehicle at the time of access to the in-vessel components is accurately carried out due to one degree of freedom defined by the running of the vehicle on the rail and that the in-vessel components are efficiently transported. An example of the rail-mounted devices is disclosed in the thesis titled "VEHICLE CONCEPT FOR NET IN-VESSEL INSPECTION AND MAINTENANCE" by D. Maisonnier (Proceedings of a Technical Committee Meeting on Robotics and Remote Maintenance Concepts for Fusion Machines--Karlsruhe, 22-24 February 1988, issued by The International Atomic Energy Agency).
Maisonnier's system comprises two boom rails extended through 90.degree. in the torus space. The boom rails are inserted therein through the opposed maintenance ports and connected at their front ends to form a vehicle-guiding rail extending through 180.degree. in the torus space. Each boom rail comprises three curved box-like link elements serially articulated at their ends to one after another. Maisonnier's thesis only briefly describes that the joint of each link member is driven by a lever mechanism and depicts that each link element contains a drive rod for driving the corresponding joint. The vehicle moves radially outwardly along the rail.
In the rail system, the semi-circularly extended rail is supported on its both ends so that the rigidity can be made larger than the articulated arm as shown in FIG. 35.
However, the semi-circularly arcuated rail is supported only on both ends and it cannot be supported at its central portion because the vehicle is moved along the radially outer side of the rail. When a heavy in-vessel component is handled by the vehicle at the central portion of the rail, a large bending moment and a large torsional moment are exerted on and at the vicinity of the end portion of the rail at which the rail is supported so that the rail is likely to be bent. Therefore, the arcuated links forming a boom rail must be rendered large in size as well. For example, when the radius curvature of the rail is 5,200 mm, the height, the width and the length of the links should be 1,000 mm, 150 mm and 2,250 mm, respectively. A large space for storing the rail is required. Further, the rail requires complicated mechanisms such as lever mechanisms for extending and shrinking the rail and drive rods. This requires complicated control when the rail is extended in the vessel.
A circular arc telescope type rail system can be used to extend a rail in the torus space. However, it has the drawback that its reliability is lowered when it remains exposed under radiation of a high level during a long maintenance time, because an actuator or a complicated driving mechanism must be provided in the rail.
Further, the thickness of the telescope rail is not constant throughout the whole length. This makes it difficult to guide and move the vehicle in a stable state and makes the structure and the control of the rail complicated.